the pump's right here, yeah? why is it when you get your blood pressure checked, they put the little doohickey on your arm, right here, right next to the arm, right, the ticker, huh? same depth. so the pressure in your arm here would be the same pressure here. but more pressure on your feet. next time you're doing that, stand on your arm-- get in the doctor's office and do a handstand. i said--tell them do it, they won't do it, okay? [laughter] that's not good. gonna talk about buoyant force. buoyant force. you walk into a pond and you grab a big boulder. and you can hold that boulder up pretty well as long as you're under the water, yeah? but you start to walk out of the pond, you carry the boulder with you, you find out the boulder gonna get heavy and heavier, yeah? some will say, "oh, the gravity is not pulling so hard in the water." what do you think? yeah. it turns out, under the water, the boulder seems to be lighter. i can show you that here. here's a boulder or a piece of metal, yeah?